Fuel cells utilize the chemical reaction of a fuel with oxygen to form water in order to generate electric energy. For this purpose, the core component of fuel cells is the so-called membrane electrode assembly (MEA), which consists of an ion-conductive (usually proton-conductive) membrane and an electrode (anode and cathode) arranged on each side of the membrane. Moreover, it is also possible to arrange gas diffusion layers (GDL) on both sides of the membrane electrode assembly on the sides of the electrodes facing away from the membrane. As a rule, the fuel cell is formed by a plurality of stacked MEAs whose electric outputs are cumulative. As a rule, there are bipolar plates (also called flow field plates) arranged between the individual membrane electrode assemblies and they ensure that the individual cells are supplied with the operating media, in other words, the reactants, in addition to which they also serve for cooling purposes. Moreover, the bipolar plates establish an electrically conductive contact with the membrane electrode assemblies.
During operation of the fuel cell, the fuel, especially hydrogen H2 or a gas mixture containing hydrogen, is fed to the anode via a flow field of the bipolar plate that is open on the anode side, where an electrochemical oxidation of H2 to form H+ takes place while electrons are released. A (hydrous or anhydrous) transport of the protons H+ from the anode space into the cathode space takes place via the electrolytes or the membrane which separates the reaction spaces and electrically insulates them from each other in a gas-tight manner. The electrons provided on the anode are fed to the cathode via an electric line. Oxygen or a gas mixture containing oxygen (for instance, air) is fed to the cathode via a flow field of the bipolar plate that is open on the cathode side so that a reduction of O2 to form O2− takes place while electrons are picked up. At the same time, the oxygen anions react in the cathode space with the protons that have been transported via the membrane, a process in which water is formed.
In order to supply the fuel cell stack with its operating media, in other words, the reactants, the fuel cell stack has, on the one hand, an anode gas supply system and, on the other hand, a cathode gas supply system. The anode gas supply system comprises an anode supply path for feeding an anode operating gas into the anode spaces of the stack, and an anode exhaust gas path for discharging an anode exhaust gas out of the anode spaces. By the same token, the cathode gas supply system comprises a cathode supply path for feeding a cathode operating gas into the cathode spaces, and a cathode exhaust gas path for discharging a cathode exhaust gas out of the cathode spaces of the fuel cell stack.